14887954cSChangbin Du.. SPDX-License-Identifier: GPL-2.0 24887954cSChangbin Du 34887954cSChangbin Du=========================== 44887954cSChangbin DuLow Power Idle Table (LPIT) 54887954cSChangbin Du=========================== 64887954cSChangbin Du 74887954cSChangbin DuTo enumerate platform Low Power Idle states, Intel platforms are using 84887954cSChangbin Du“Low Power Idle Table” (LPIT). More details about this table can be 94887954cSChangbin Dudownloaded from: 104ce77966SAlexander A. Klimovhttps://www.uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdf 114887954cSChangbin Du 124887954cSChangbin DuResidencies for each low power state can be read via FFH 134887954cSChangbin Du(Function fixed hardware) or a memory mapped interface. 144887954cSChangbin Du 154887954cSChangbin DuOn platforms supporting S0ix sleep states, there can be two types of 164887954cSChangbin Duresidencies: 174887954cSChangbin Du 184887954cSChangbin Du - CPU PKG C10 (Read via FFH interface) 194887954cSChangbin Du - Platform Controller Hub (PCH) SLP_S0 (Read via memory mapped interface) 204887954cSChangbin Du 214887954cSChangbin DuThe following attributes are added dynamically to the cpuidle 224887954cSChangbin Dusysfs attribute group:: 234887954cSChangbin Du 244887954cSChangbin Du /sys/devices/system/cpu/cpuidle/low_power_idle_cpu_residency_us 254887954cSChangbin Du /sys/devices/system/cpu/cpuidle/low_power_idle_system_residency_us 264887954cSChangbin Du 274887954cSChangbin DuThe "low_power_idle_cpu_residency_us" attribute shows time spent 284887954cSChangbin Duby the CPU package in PKG C10 294887954cSChangbin Du 304887954cSChangbin DuThe "low_power_idle_system_residency_us" attribute shows SLP_S0 314887954cSChangbin Duresidency, or system time spent with the SLP_S0# signal asserted. 324887954cSChangbin DuThis is the lowest possible system power state, achieved only when CPU is in 334887954cSChangbin DuPKG C10 and all functional blocks in PCH are in a low power state. 34